The use of turbines designed to transform wind energy into mechanical energy is well known, such devices generally being arranged in arrays comprising a significant number of turbines erected in particularly windy locations.
Generators of known type usually comprise a frame designed to rotatingly support fluid-dynamic means destined to capture the wind, the fluid-dynamic means being connected by a mechanical transmission to a user device, for example a generator of electrical current.
The kinetic energy of the air is generally converted into mechanical energy and subsequently into electrical energy using aerogenerators.
Installations range comprises from mini- and micro-scale wind turbines which give an output of from a few hundred Watts to tens of kW of power, to medium sized installations rendering up to about a hundred kW, and finally to large scale systems which can produce an output measured in MW.
Horizontal axis machines of known type exhibit a rotor axis parallel to the direction of the wind and a rotor which rotates on a plane perpendicular to the direction of the wind.
Such devices can be further sub-categorized according to the characteristics of the rotor.
While numerous variants exist, the typical rotor is normally characterized by a wing shaped radial blades.
The special characteristics of the machine are high rotational speed and high power output as a consequence of the high lift coefficient of the blades.
Also known are vertical axis machines exhibiting a rotor axis that is placed perpendicular to the direction of the wind.
Again these can be sub-categorized on the basis of the rotor type used.
In this specific configuration the turbine exhibits the considerable advantage of not needing to orientate itself relative to the direction of the wind, which can thus be exploited around 360° of rotation without auxiliary movements. In contrast, the rotor of horizontal axis machines must be guided to face the direction of the wind using a vane.
Vertical-axis machines are of limited dimensions and are more suited to urban wind patterns which are normally turbulent, extremely variable in direction and strength, and consequently badly suited to horizontal axis turbines.
Vertical axis turbines are also suitable for use in very remote locations characterized by extreme climactic conditions including the formation of ice and intense, variable wind patterns.
Generators of known type exhibit a number of disadvantages which to date have not been successfully resolved.
A first disadvantage is aesthetic, since in order to provide an acceptable level of power wind turbines must be arranged in arrays or “farms” comprising a considerable number of turbines.
Wind farms must be positioned in windy areas and unavoidably compromise landscape which is often of considerable environmental relevance, and their construction is understandably opposed by local authorities.
Environmental impact is worsened by the fact that the air currents required to turn the fluid-dynamic means of the turbines are generally found at a significant height above ground, making it necessary to construct turbines of a considerable height.
An efficient height is thought to be at least 6 meters above ground level in order to achieve acceptable results.
A second disadvantage, technical in nature, is the limited yield of known fluid-dynamic means which are efficient only if the wind speed is above approximately 6 m/sec., a velocity that is rarely encountered in proximity to urban areas, and consequently any generated electricity is subject to significant transport costs.
Consequently there is an obvious need for a wind turbine, of limited bulk in both the horizontal and vertical profiles, that can operate with wind at a lower speed than that required to drive generators of known type while providing a comparatively higher energy yield.